Evidence for selection on a CONSTANS-like gene between two red oak species

• Published in: Annals of botany Vol. 113; no. 6; pp. 967 - 975
• Main Authors: Lind-Riehl, Jennifer F, Sullivan, Alexis R, Gailing, Oliver
• Format: Journal Article
• Language: English
• Published: England Oxford University Press 01.05.2014
• Subjects: adaptive radiation; Alleles; chromosome mapping; drought; drought tolerance; Ecological genetics; Evolutionary genetics; Flowering; Gene flow; genes; Genes, Plant; Genetic loci; growth and development; high-throughput nucleotide sequencing; loci; microsatellite repeats; Oak trees; Original; Outliers; phenology; Population genetics; Quercus; Quercus - classification; Quercus - genetics; Quercus rubra; reproductive isolation; Speciation; Species Specificity; speciation genes; divergent selection; like genes; red oak; ecological speciation; flowering time; Q. ellipsoidalis; Quercus rubra; CONSTANS-like genes
• ISSN: 0305-7364; 1095-8290
• DOI: 10.1093/aob/mcu019

Background and AimsHybridizing species such as oaks may provide a model to study the role of selection in speciation with gene flow. Discrete species' identities and different adaptations are maintained among closely related oak species despite recurrent gene flow. This is probably due to ecologically mediated selection at a few key genes or genomic regions. Neutrality tests can be applied to identify so-called outlier loci, which demonstrate locus-specific signatures of divergent selection and are candidate genes for further study.MethodsThirty-six genic microsatellite markers, some with putative functions in flowering time and drought tolerance, and eight non-genic microsatellite markers were screened in two population pairs (n = 160) of the interfertile species Quercus rubra and Q. ellipsoidalis, which are characterized by contrasting adaptations to drought. Putative outliers were then tested in additional population pairs from two different geographic regions (n = 159) to support further their potential role in adaptive divergence.Key ResultsA marker located in the coding sequence of a putative CONSTANS-like (COL) gene was repeatedly identified as under strong divergent selection across all three geographically disjunct population pairs. COL genes are involved in the photoperiodic control of growth and development and are implicated in the regulation of flowering time.ConclusionsThe location of the polymorphism in the Quercus COL gene and given the potential role of COL genes in adaptive divergence and reproductive isolation makes this a promising candidate speciation gene. Further investigation of the phenological characteristics of both species and flowering time pathway genes is suggested in order to elucidate the importance of phenology genes for the maintenance of species integrity. Next-generation sequencing in multiple population pairs in combination with high-density genetic linkage maps could reveal the genome-wide distribution of outlier genes and their potential role in reproductive isolation between these species.